Mutation theory was proposed by.

Hugo de Vries a Dutch botanist and geneticist studied the inheritance of flower colour in Evening Primrose and found the sudden and random appearance of new characters as mutation. He proposed mutation theory that says that mutations are sudden, random, inheritable and dicontinuous variation which serve as raw material for evolution.

Whereas Mendel conducted hybridization experiment on garden pea plant, pisum sativum and proposed the “Law of inheritance”.

Also, Lamarck proposed the theory of inheritance of acquired characteristics, using the example of short neck giraffes evolving into the long neck giraffes.

Kolreuter discovered the pollination of plants by insects to study inheritance in plants.

Hence, the correct answer is option ( A ) Hugo de Vries.